IPv6 (Internet Protocol Version 6) is a next generation internet protocol replacing the current internet protocol IPv4 (Internet Protocol Version 4). Advantages of IPv6 with respect to IPv4 are: a larger address space, smaller routing tables and additional supports for enhanced multicast and for stream, and thus IPv6 has a considerable development opportunity and provides a great network platform for service quality control. Therefore, how to migrate network data in IPv4 network to IPv6 network is a key problem in present network service researches.
The conventional method for data migration between IPv4 and IPv6 includes the following three ones:
(1) Dual Stack Technology
As shown in FIG. 1, the dual stack requires that all network devices in the data center system should be equipped with IPv4/IPv6 internet protocol, which has a high deployment cost and some old devices do not support the IPv6 internet protocol. In addition, the dual stack has a high requirement for the network's own performance, and many existing devices are not evaluated for IPv6, and thus the risk is uncontrollable. In the dual stack technology, the IPv4 network and the IPv6 network are independent from each other, and a data communication between each other is blocked.
(2) NAT (Network Address Translation) 64/DNS (Domain Name System) 64
NAT64 is a stateful network address and protocol translation technology, which generally supports initiating a connection from an IPv6 user to access IPv4 resources. However, NAT64 also supports initiating a connection from the IPv4 user to access IPv6 resources actively via manually configuring static mappings. NAT64 can realize the network address and protocol translation between IPv6 and IPv4 under the TCP (Transmission Control Protocol), UDP (User Datagram Protocol) and ICMP (Internet Control Message Protocol). DNS64 mainly cooperates with the NAT64 to synthesize an A recording (IPv4 address) in DNS query information into an AAAA record (IPv6 address), and to return the synthetic AAAA record to the IPv6 user. DNS64 also avoids the defects of DNS-ALG in NAT-PAT. NAT64 commonly cooperates with DNS64 and no modification is required in the IPv6 client or in the IPv4 server. NAT64 solves most of the defects in NAT-PT and cooperates with DNS64, which is different from the DNS-ALG in NAT-PT.
FIG. 2 illustrates a common application scene network of NAT64 and DNS64. As shown in FIG. 2, a DNS64 server and a NAT64 router are independent from each other, in which 64:FF9B::/96 is a domain name prefix special of DNS64 and is commonly defaulted to be used to synthesize the network address from the IPv4 address to the IPv6 address, meanwhile the domain name prefix can also be used as a translation prefix of NAT64, and only when a traffic matching with the prefix is achieved, can the NAT64 translation be performed. This prefix is commonly denoted as pref64::/n, and can be configured according to practical network deployments. When the IPv6 user initiates a connection to access common IPv6 websites, the traffic is matched to an IPv6 default route and is forwarded to an IPv6 router directly. When the IPv6 user initiates a connection to an IPv4 single stack server, the address is synthesized with the domain name prefix by the DNS64 server, and the traffic in pref64::/n network segment is routed to the NAT64 router, thus achieving the network address and protocol translation between IPv4 and IPv6 and accessing resources in IPv4 network.
FIG. 3 illustrates a message interaction process between DNS64 and NAT64. As shown in FIG. 3, structures of a network address are shown as follows:
IPv6 Only Client: 2001::1234::1234;
Pref64::/n: 64:FF9B::/96
NAT64 Public IPv4 Address: 22.22.22.22
WWW.IPV6BBS.CN IPv4 Address: 11.11.11.11
Defects of NAT64/DNS64 are shown as follows:                (A) A strong coupling with DNS is required;        (B) Only a connection initiated by the IPv6 user to access IPv4 resources is supported, being commonly deployed at the user side;        (C) Stateful address mappings exist;        (D) A large number of public IP addresses are required in the address pool.        
(3) IVI (The Transition to IPv6)
FIG. 4 illustrates a one to one mapping between IPv6 address subsets and IPv4 addresses. As shown in FIG. 4, IPv6 address subsets are mapped with the IPv4 addresses one to one, such that the mapped address subset and IPv6 address can communicate with each other. However, the IVI has following defects:
(A) IVI is not adapted to be applied in IDC (Internet Data Center);
(B) A strong coupling with DNS is required;
(C) IVI is commonly deployed in an ISP (Internet Service Provider) network.
Accordingly, the conventional methods for data migration between IPv4 and IPv6 have a high deployment cost, a high risk and a certain deployment limitation, which may not satisfy the migration requirement of the large scale data center.